Fixed a bug affecting min/max vector computations

While checking into the source code of psmoveapi.c, just to take a look at this project and see a little bit about how it works, I ran into a pair of defects. Since comparing vector.y > vector.y seemed like an honest mistake I figured this was a bug. After asking about this in https://github.com/thp/psmoveapi/issues/138 and having this confirmed as an issue, I figured I'd submit a pull request to patch it.

First pull request to an open source project, so please let me know if there's any practices I can improve upon in doing so!